Liquid neoalkylpolyol esters of mixtures of neo-and straight or branched chain alkanoic acids and their preparation

ABSTRACT

NEOALKYLPOLYOL ESTERS OF MIXTURES OF STRAIGHT CHAIN FATTY ACIDS OR BRANCHED CHAIN FATTY ACIDS WHICH ARE NOT NEO ACIDS, AN NEOALKYL FATTY ACIDS ARE PREPARED BY A NOVEL PROCESS WHICH RESULTS IN A PRODUCT HAVING SUPERIOR LOW TEMPERATURE PROPERTIES AND OXIDATION STABILITY. THE NOVEL PROCESS OF THIS INVENTION COMPRISES PARTIALLY ESTERIFYING A NEOALKYLPOLYOL WITH A MIXTURE OF STRAIGHT CHAIN OR BRANCHED CHAIN CARBOXYLIC ACIDS AND A NEOALKYL FATTY ACIDS, REMOVING UNREACTED ACID FROM THE MIXTURE BEFORE THE ESTERIFICATION IS COMPLETE, AND ADDING STRAIGHT OR BRANCHED CHAIN FATTY ACID SUFFICIENT TO COMPLETE THE ESTERIFICATION.

Unitedstates Patent omee 3,5623% Patented Feb. 9, 1971 LIQUID NEOALKYLPOLYOL ESTERS F MIX- TURES 0F NEO- AND STRAIGHT 0R BRANCHED CHAIN ALKANOIC ACIDS AND THEIR PREP- ARATION Tai S. Chao, Homewood, Ill., and Manley Kjonaas, Hammond, Ind., assignors to Sinclair Research, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 9, 1967, Ser. No. 673,932

Int. Cl. (30% 53/00, 53/22 U.S. Cl. 260398 16 Claims ABSTRACT OF THE DISCLOSURE Neoalkylpolyol esters of mixtures of straight chain fatty acids or branched chain fatty acids which are not neo acids, and neoalkyl fatty acids are prepared by a novel process which results in a product having superior low temperature properties and oxidation stability. The novel process of this invention comprises partially esterifying a neoalkylpolyol with a mixture of straight chain or branched chain carboxylic acids and a neoalkyl fatty acid, removing unreacted acid from the mixture before the esterification is complete, and adding straight or branched chain fatty acid suflicient to complete the esterification.

This invention is concerned with liquid synthetic esters, prepared by the novel process of this invention, which are useful, for instance, as base fluids for lubricants, and functional fluids such as plasticizers. More specifically, this invention is concerned with certain neoalkylpolyol esters which are prepared by stepwise esterification of mixtures of straight or branched chain fatty acids other than neo acids and neoalkyl fatty acids and which possess superior low temperature properties and oxidation resistance. Improved low temperature storage stability has important bearing on the use of esters in jet aircraft lubricants and in functional fluids and plasticizers which are subjected to low temperature environments. In jet aircraft engines, any crystallization and solidification of the lubricant may plug up lubricant supply lines, freeze up moving parts and make the lubricant unavilable to the bearings during the critical start-up time. The results can be disastrous. Similarly, crystallization and solidification in functional fluids will cause plugging of supply lines, exert excessive load on the pumps and interefere with their ability to transmit power or heat. Also, plasticizers which solidify when cooled will not impart the desired flexibility to polymers which in themselves are often brittle at low temperatures.

Lubricants composed in whole or in part of synthetic components have been developed in an effort to obtain superior lubricating compositions. In general, these lubricating compositions are characterized by higher viscosity indices, lower pour point and greater heat stability than mineral oils of corresponding viscosity. Such properties are of special value in lubricating engines which are subjected to high temperatures, such as combustion turbine engines.

Mineral oil lubricants, even those containing added VI improvers, pour point depressors, it other additives are undesirable for use in such engines because of the relatively high volatility, low flash point, and poor thermal and oxidative stability of the mineral oil which also has a tendency to leave deposits which accumulate and interfere with the operation of the engine.

Certain neoalkylpolyol esters of straight chain fatty acids, e.g. pentaerythritol tetracaproate, which are known as Type II lubricants, have been employed in jet engines but do not possess the thermal and oxidative stability required of the more advanced engine models. On the other hand, esters derived from neoalklpolyols and branchedchain fatty acids, e.g., pentaerythritol tetrapivalate, although having good oxidative stability, are solids at room temperatures and thus have poor handling, starting and low temperature properties. Polyphenyl ethers, e.g., m,m,m bisphenoxy phenoxybenzene, have pour points above 3540 F. and do not flow and pour at sub-zero temperatures, as required to achieve their functions, especially during the critical start up time for jet engines.

Various liquid esters such as di-Z-ethylhexyl sebacate, etc., have been used commercially in or as lubricants. In particular, esters of neoalkyl fatty acids and neoalkylpolyols of 3-5 hydroxyl groups such as trimethylol-propane and pentaerythritol have generally been good base fluids for high temperature synthetic lubricants. The presence of alkyl groups and the absence of H-atoms on the a-carbon atom impart many unique properties to neoalkyl fatty acid esters such as increased thermal, oxidative and hydrolytic stability. This increased stability renders them highly desirable for use as base fluid for jet engine lubricants, functional fluids, greases and as plasticizers. However, the presence of the alkyl groups on the a-carbon atoms also imparts some severe disadvantages. The first disadvantage is due to the steric hindrance exerted by the alkyl groups on esterification, with the consequent need for more drastic conditions which increase processing costs and result in inferior products. The second and much more damaging effect is that, despite having greater thermal stability than straight chain acid esters, they also have higher melting points. Further, the successful use as lubricants of esters of neoalkyl fatty acids and neoalkyl polyols has been extremely limited, since most of them have been known to exist as solids at room temperature, this being especially true for the plural esters such as those wherein 3 or more of the hydroxyl groups of the alcohol are esterified.

Properties of pentaerythritol esters of straight chain acids and pentaerythritol esters of neo-acids prepared by conventional, one-step esterification procedures are compared in Table I. It can be seen that the PE ester of the neo-acids have M.P. of 1493 10 F. and cannot be used as base fluid for jet engine lubricants which require a pour point of -20 to 60 F. Their usefulness as functional fluids which often require operation at sub-zero temperatures, and as plasticizers which must impart low temperature flexibility to polymers is also limited. Data in Table I also show that esters of neo-acids have lower flash point and hence greater volatility than their straight-chain isomers.

TABLE I.PHYSICAL PROPERTIES OF PENTAERYTHRI- 'IOL (PE) ESTERS OF STRAIGHT-CHAIN VS. NED-ACIDS Kinematic viscosity, cs. Pour Flash M.P., point, point, 210 40 Ester F. F. F. F. F. F.

PE tetra n-C5 Liquid.. 80. 465 3.727.. 17. 29.. 3,539. PE tetra neo-C5 258-62... Solid Solid.. Solid.. Solid.

PE tetra n-Cu Liquid" 70... 475 4.136.- 19.59-. 4,128. PE tetra neo-Ca 300-10-.. Solid Solid.. Solid.. Solid.

PE tetra n-C7 Liquid.- -30..- 530 4. 717.. 23. 28.. PE tetra neo-C 189-92... Solid.. 440 8.171.. Solid Solid.

PE tetra l'l-Cs Liquid" 0 530 5. 345.. 27.86.. PE tetra neo-O 149-53... Solid.. 470 13.19.. Solid Solid.

1 Too viscous to measure.

Liquid esters have also been prepared conventionally from neopentylpolyols with mixtures of neoand straightchain acids, however, studies indicated that a high percentage of the straight-chain acid must be used, with a corresponding sacrifice in oxidation resistance. Thus, pentaerythritol esters of mixtures of neoheptanoic and nvaleric acids containing less than 50 mole percent nvaleric groups (as determined by NMR) have poor low temperature stability. This is because the ester product is usually a mixture containing all possible single esters such as tetra-neo-C tetra-n-C trio-neo-C -mono-n-C di-neo- C di-n-C etc. and the tetra-neo-C having a M.P. of 189l92 P. will crystallize out of this mixture upon standing, especially at low temperatures.

It has now been found, in accordance with the present invention, that neoalkylpolyol esters of mixtures of neoalkyl fatty acids and straight chain acids or branched chain acids which are not neo acids, when prepared by the novel method of this invention, possess, in addition to desirable properties of both neo and straight chain acid esters, excellent low temperature properties such as stability and oxidation stability, even when more than 50% neo acid is employed.

In accordance with the process of this invention, the esters of this invention are prepared by esterifying a neoalkyl polyol of up to or 12 or more carbon atoms and 2 to 6 hydroxy groups and preferably not more than 7 carbon atoms and 2 to 4 hydroxy groups, such as, for example, pentaerythritol, dipentaerythritol, anhydroenneaheptitol, or 1,1,1-trimethylolalkanes of 5 to 7 carbon atoms with straight chain alkanoic carboxylic acids having from 4 to 12 carbon atoms or branched chain alkanoic carboxylic acids of 4 to 12 carbon atoms other than neo acids and a neo alkanoic acid having 5 to carbon atoms and preferably 5 to 10 carbons, and the general formula:

in which R R and R are alkyl groups of 1 to 6 carbon atoms and R and R are preferably 1 to 4 carbons, particularly methyls. Examples of suitable neoalkyl acids are 2,2-dimethylpropanoic, 2,2-dimethylbutanoic, 2,2-dimethylpentanoic, 2,2-dimethylhexanoic, and 2,-dimethyloctanoic acids. The esterification of the neoalkyl polyol with the neo and straight or branched chain acids is carried out using a mole ratio of neoalkyl polyol to straight or branch chain acid to neo acid of 1:1.52:38 and is allowed to proceed until 8090% completion as judged from the quantity of water formed. At this point the remaining unreacted acids are removed by distillation, preferably under reduced pressure. Following removal of the unreacted acids, suflicient straight chain alkanoic carboxylic acid of from 4 to 12 carbon atoms is added to complete the esterification.

The esterification is preferably carried out in the presence of an inert gas such as N and at temperatures of 1502l0 C. and in the presence of a solvent to facilitate mixing during the earlier stages of esterification and to aid water removal via azeotropic distillation. Suitable solvents include xylene, toluene, ethylbenzene and aliphatic hydrocarbons having comparable boiling points.

Purification, if desired of the reaction mixture can then be accomplished by distillation under vacuum to remove any excess acid, and washing successively with aqueous Na CO or other suitable alkali reagents, and water, drying under vacuum, and filtering to give a clear liquid ester.

The reaction is usually carried out in the absence of a catalyst. However, catalysts which do not interfere with the suitability of the finished ester for the intended use can be used. Sulfuric acid, p-toluene sulfonic acid and other sulfur-containing acids are generally avoided in the preparation of esters intended for use as base fluid for synthetic lubricants. These acids can be used, however, if the ester is to be used as a plasticizer and a functional 4 fluid. Other catalysts which may be used include phosphoric acids, organo-tin compounds, titanium esters, acidic ion-exchange resin, acidic clay and crystalline alumino silicates.

The esterification may be carried out using conventional esterification equipment which may consist of a reaction vessel made of materials resistant to organic acids (such as glass or stainless steel), a stirrer, a reflux condenser, and an azeotrope trap.

Neo acids employed in this invention can be prepared by the process in which a 2-alkyl olefin is condensed with CO and H 0 in the presence of acidic catalysts, such as H PO and BF;;, to give the desired product or they may be prepared by the treatment of a tertiary Grignard reagent with CO followed by hydrolysis.

The following examples further illustrate the process covered in this invention.

EXAMPLE I Preparation of pentaerythritol neoheptanoate n-valerate (Ester A) A mixture of 272 g. (2.0 moles) of pentaerythritol, 408 g. (4.0 moles) n-valeric acid, 1040 g. (8.0 moles) of neoheptanoic acid and 200 g. of xylene was placed in a 2-liter, 4-necked flask equipped with a mechanical stirrer, a reflux condenser and a Dean-Stark azeotrope trap. The mixture was refluxed at 156178 C., with constant stirring and under the protection of N for a period of 22 hours. During this period a total of 115.5 ml. of theory) of water was collected from the trap. The mixture was distilled under vacuum to remove the unreacted acids, the final temperature and pressure being 175 C. and 1 mm. Hg. To the residue was added 204 g. (2 moles) of n-valeric acid and 200 g. of xylene. Esterification was continued at 173-l80 C. for another 33 hours during which an additional 28.5 ml. (20% of theory) of water was collected. The reaction mixture was vacuum distilled to remove remaining acid and then Washed twice with 5% Na CO solution. The ester was then stirred with 6 g. of

NaBH and ml. of 0.1 N NaOH at 50-60 C. for about 20 hours under a N atmosphere. Upon cooling and settling, the aqueous layer was removed and the ester layer was diluted with xylene and washed twice with water. The washed solution was vacuum distilled and the residue was treated with 50 g. of Attapulgus Fines (a decolorizing clay) for 2 hrs. at 100-110 C. and filtered through Hyflo Super-Cel (a diatomite filter aid). There was obtained about 750 g. of a light yellow clear viscous liquid which will be called Ester A in subsequent discussions.

EXAMPLE 11 Preparation of pentaerythritol neoheptanoate n-caproate (Ester B) A mixture of 2 moles of pentaerythritol, 4 moles of n-caproic acid, 8 moles of neoheptanoic acid and 200 g. of xylene was similarly refluxed at -176 until 122 ml. (84.6%) of water was collected in the Dean-Stark trap (43 hrs.). After removal of unreacted acids by vacuum distillation 116 g. (1 mole) of n-caproic acid and 100 g. of xylene were added. Esterification was continued at -7 until no more water was collected (18 hrs.). The reaction mixture was worked up in the same manner as described in Example I, yielding 940 g. of light yellow clear liquid which will be called Ester B in subsequent discussion.

EXAMPLE III Preparation of a liquid pentaerythritol ester (Ester C) from a mixture of neoheptanoic, n-valeric, isovaleric, n-caproic and n-heptanoic acids A mixture of 1 mole (136 g.) of pentaerythritol, 3 moles of neoheptanoic acid and 0.5 mole each of n-valeric, isovaleric, n-caproic and n-heptanoic acids was refluxed with 125 g. of xylene in the same manner as described 5 above. After 39.5 hrs. at 173182, a total of 58 ml. (80% of theory) of water was collected in the trap. After removal of the unreacted acids and xylene, 163 g. (1.5 moles) of n-valeric acid and 125 g. of xylene were added and esterification was completed after another 31.5 hrs. at 171-181". The reaction mixture was worked up in the TABLE II.--PHYSICAL PRggE 6 be seen that the esters A, B and C have superior low temperature properties to esters D and E or the neo-acid esters shown in Table I. The pour points are lower, the viscosity at and 40 F. are lower and the esters of this invention remained clear liquids during low temperature storage tests at 20, 0, 30 and 60 F.

R'IIES OF PENTAERYTHRITOL NED-ACID ESTERS PRE- RED BY DIFFERENT METHODS Identity Ester A Ester B Ester C Ester D Ester E Acids other than neoC1 11-05 n-C n-C5, i-C5, n-O n-C5.

n-Cs n-C1. Method of preparation New New New Conventional Conventional. Kinematic v1s., c.s.:

210 F 4 744 4 988 4.854 o .45 5 218 100F 29. 1 0 F -40 F Fire point,F 520. Appearance after 60 hrs Clear liquid Clear liquid Clear alized Crystalized. 2 F do ,rln do dn Do.

F"--. d0 do do do. Do. 30 F D0. -60 F .do .do do o D0- 1 Too viscous to measure.

2 supercooled.

3 Micro-scale.

same manner as described in Example I, yielding a light yellow clear liquid which will be referred to as Ester C. The yield before the NaBH and clay treatment was 507 g.

In addition to these three esters, two other esters, D and E, were also prepared employing conventional, one step, preparative procedures.

Ester D was prepared by the same procedure as shown in Example I except that esterification was completed in one step and a larger excess of neo-C acid was used. The ester was a liquid when first prepared, but crystals started to appear after a few days storage at room temperature. When a 4 02. sample was placed in a refrigerator (temperature F.), solidification occurred in a few hours. The mass consisted of a mixture of needle-like crystals and viscous liquid and could not be poured without stirring. The same crystalline mass was observed after storing in low temperature baths for 60 hrs. at 0, -30 and -60 F. Under the same low temperature storage conditions Ester A remained as clear pourable liquid.

Ester E was prepared as shown in Example IV in order to insure that the low temperature storage stability attributed to Ester A was not due to the reduced amount of excess neoheptanoic acid used in its preparation.

EXAMPLE IV Preparation of pentaerythritol neoheptanoate n-valerate (Ester E) A mixture of 272 g. (2 moles) of pentaerythritol, 408 g. (4.0 moles) of n-valeric acid, 1040 g. (8.0 moles) of neoheptanoic acid and 200 g. xylene was placed in a 3-liter, 4-necked flask and stirred at reflux temperature until 14 ml. (100% of theory) of water was collected from the trap. The mixture was distilled under vacuum to remove the solvent and the excess acid. The residue was diluted with exylene and washed twice with 5% Na CO solution and twice with water. The washed solution was topped to 165 1 mm., leaving 913 g. of residue which was then filtered through diatomaceous earth.

The product showed a slightly better low temperature property than Ester D. However, the same low temperature instability was observed. Crystallization took place when the ester was placed in refrigerator or in low temperature baths at 0, 30 and 60 F. The pour points shown by Esters D and E are due to super cooling resulting from the short period of time given to the esters in carrying out the pour point determination. When sufficient time was given, crystallization took place and the esters can no longer be poured.

Table II shows physical properties of esters A, B and C prepared by the method of this invention and esters D and E prepared by conventional procedures. It may Table III shows the oxygen absorption test results of the three esters (A, B and C) prepared by the method of this invention. A typical ester of a straight chain fatty acid used as a base fluid for Type 2 synthetic lubricants, Ester F, is shown for comparison.

The Oxygen Absorption Test is a test designed to determine the oxidation resistance of lubricants. In principle it resembles the Dornte Oxygen Absorption Test (see WADC Tech. Report 59-191, part III, pp. 30-32) and measures the rate of oxygen consumption by the lubricant at a given temperature. Briefly, a weighed sample of the lubricant is placed in a Pyrex oxidation cell which is heated electrically in an aluminum block. Oxygen gas is bubbled through the lubricant at a specified rate. The exit gases go through a series of absorbants and a tube furnace so that all C0, C0 H 0 and organic materials were removed, leaving only the unconsumed oxygen which is circulated again through the hot lubricant. As the lubricant is oxidized and oxygen is used up, the pressure in the closed system drops. This pressure drop which is directly proportional to the volume of O consumed is constantly monitored and recorded. A curve is obtained which indicates the volume of oxygen consumed vs. time. A lubricant of good oxidation resistance usually shows a very low rate of oxygen consumption at the beginning. As oxidation proceeds, the inhibitors will gradually be used up and the pro-oxidation species (such as peroxy radicals) will accumulate. At one point the rate of oxidation will increase drastically and the curve makes a sharp bend. The time required for this to happen is generally called induction time (T When a specified volume (V of 0 has been consumed, the unit is shut down automatically. The time for this to happen is called total time (T The used oil is then analyzed for acid number and viscosity and, sometimes, pentane insolubles. Therefore, this test also furnishes information on the extent of oxidative degradation (as indicated by increases in acid number and viscosity) upon the consumption of a definite amount of oxygen by the lubricant. This last-named property is often called oxygen tolerance. A lubricant of good oxygen tolerance and low rate of oxidation (high T, and T generally will show less oxidative degradation in a bearing rig and in service. The amount of stain or deposit on the wall of the oxidation cell can often be used to predict the cleanliness of the lubricant in rig tests, although this relationship is not as reliable as the relationship mentioned above.

It can be seen that all three esters of this invention have T, and T considerably longer than those of ester F and the viscosity increases, A(KV/ were considerably lower. This indicates that the three base fluids prepared by the method of this invention have a lower rate of oxidation in presence of the common inhibitor and, when oxidized to the same extent (2500 ml. absorbed), gave lower increase in viscosity than the Type 2 base fluid. A comparison between results of Esters A and D also indicates that the present process, while greatly improving the low temperature properties of the mixed esters, did not detract from the gOOd oxidation resistance inherent in the mixed neo-C -n-C esters.

TABLE III.-OXYGEN ABSORPTION TEST RESULTS OF PENTAERYTHRITOL NEO ACID ESTERS PREPARED BY METHOD OF THIS INVENTION [Temperature=450 F.; Oxygen rate=1 itfi/hiz; Inhibit0r=1% N-phenyll-naphthylamine] Ester Ester Ester Ester Ester Base Fluid A B C D F 1 Results:

'1,, min.-- 413 390 353 442 200 T min 473 437 393 482 242 V;, ml 575 537 537 (300 466 Vt, ml 2, 500 2, 500 2, 500 2, 500 2, 500 A (KV/IOO), percent 37. 5 41. 37. 3 36. 1 49. 7 A (a.n.) 11.2 14.1 11.8 13.1 10. 1

1 Hercolube A.

We claim:

wherein R R and R are alkyl groups of 1 to 6 carbon atoms, the mole ratio of neoalkylpolyol to said straight or branched chain alkanoic acids to said neo alkanoic acid in the mixture being 1:1.52:38, (B) removing essentially all unreacted acids from the mixture of unreacted acids and neoalkylpolyol partially esterified to not more than 90% completion,

(C) reacting sutficient straight chain alkanoic acid of from 4 to 12 carbon atoms with said partially esterfied neoalkylpolyol to complete the esterification, and obtaining as the resulting product a liquid neoalkylpolyol mixed ester.

2. The process of claim 1 in which the neoalkylpolyol is of not more than 7 carbon atoms and has a 2 to 4 hydroxy groups.

3. The process of claim 1 in which the neoalkylpolyol is selected from the group consisting of pentaerythritol, dipentaerythritol, anhydroenneaheptitol, and 1,1,1-trimethylolalkanes of 5 to 7 carbon atoms.

4. The process of claim 1 in which the neoalkylpolyol is pentaerythritol.

5. The process of claim 1 in which R and R in the formula of the neo alkanoic acid are methyl groups.

6. The process of claim 1 in which the neo alkanoic acid is selected from the group consisting of 2,2-dimethylpropanoic, 2,2-dimethylbutanoic, 2,2-dimethylpentanoic, 2,2-dimethylhexanoic, and 2,2-dimethyloctanoic acids.

7. The process of claim 1 in which the neoalkylpolyol is pentaerythritol and the neo alkanoic acid is neoheptanoic acid,

8. The process of claim 1 in which the neoalkylpolyol is pentaerythritol, the neo alkanoic acid is neoheptanoic acid, and the straight chain or branched chain alkanoic acids are selected from the group consisting of n-valeric, isovaleric, n-caproic and n-heptanoic acids, said pentae- 8 rythritol is partially esterified to completion with said mixture of neoheptanoic and straight or branched chain alkanoic acids and said partially esterified pentaerythritol after removal of unreacted acids is completely esterified with n-valeric or n-caproic acid.

9. An oxidation resistant, stable, loW temperature liquid mixed ester of a neoalkylpolyol, of up to 12 carbon atoms and having 2 to 6 hydroxy groups, partially esterified to from 80 to completion with a mixture of straight chain or branched chain alkanoic acids, other than neo acids, of from 4 to 12 carbon atoms, and a neo alkanoic acid of 5 to 20 carbon atoms of the formula:

where R R and R are alkyl groups of 1 to 6 carbon atoms, the mole ratio of neoalkylpolyol to said straight or branched chain alkanoic acids to said neo alkanoic acid in the mixture being 1:1.52:38, and said partially esterified neoalkylpolyol, free from unreacted acids, being reacted with a straight chain alkanoic acid of 4 to 12 carbon atoms to complete esterification.

10. An oxidation resistant, stable, low temperature liquid mixed ester of a neoalkylpolyol of claim 9 in which the neoalkylpolyol is of not more than 7 carbon atoms and has 2 to 4 hydroxy groups.

11. An oxidation resistant, stable, low temperature liquid mixed ester of a neoalkylpolyol of claim 9 in which the neoalkylpolyol is selected from the group consisting of pentaerythritol, dipentaerythritol, anhydroenneaheptitol, and 1,1,1-trimethylolalkanes of 5 to 7 carbon atoms.

12. An oxidation resistant, stable, low temperature liquid mixed ester of a neoalkylpolyol of claim 9 in which the neoalkylpolyol is pentaerythritol.

13. An oxidation resistant, stable, low temperature liquid mixed ester of a neoalkylpolyol of claim 9 in which R and R in the formula of the neo alkanoic acid are methyl groups.

14. An oxidation resistant, stable, low temperature liquid mixed ester of a neoalkylpolyol of claim 9 in which the neo alkanoic acid is selected from the group consisting of 2,2-dimethylpropanoic, 2,2-dimethylbutanoic, 2,2- dimethylpentanoic, 2,2-dimethylhexanoic, and 2,2-dimethyloctanoic acids.

15. An oxidation resistant, stable, low temperature liquid mixed ester of a neoalkylpolyol of claim 9 in which the neoalkylpolyol is pentaerythritol and the neo alkanoic acid is neoheptanoic acid.

16. An oxidation resistant, stable, low temperature liquid mixed ester of a neoalkylpolyol of claim 9 in which the neoalkylpolyol is pentaerythritol, the neo alkanoic acid is neoheptanoic acid, and the straight chain or branched chain alkanoic acids are selected from the group consisting of n-valeric, isovaleric, n-caproic and n-heptanoic acids, said pentaerythritol being partially esterified to 80% completion with said mixture of neoheptanoic and straight chain or branched chain alkanoic acids, and said partially esterified pentaerythritol, free from unreacted acids, being furher completely esterified with n-valeric or n-caproic aci References Cited UNITED STATES PATENTS 2,077,371 4/1937 Rheineck et a1 260398 3,247,111 4/1966 Oberright et al. 25234.7 3,330,762 7/1967 Wendler et al. 25232.5 3,341,574 9/1967 Taylor et al 260-485 3,441,600 4/1969 Chao et a1 260-488 ELBERT L. ROBERTS, Primary Examiner US. Cl. X.R. 

